Thermal and FTIR spectroscopic analysis of the interactions of aniline adsorbed on to MCM-41 mesoporous material

The adsorption of aniline on Na-AlMCM-41 synthesized by us has been characterized by infrared spectroscopy, temperature programmed desorption (TPD), and differential thermal analysis methods. Aniline would be mostly bound to the mesostructure through weak pi interactions. On the mesostructure containing adsorbed water, the co-adsorption of aniline could occur by weak hydrogen bonding through surface water molecules. For water, two possible modes of adsorption have been identified. Different associations between aniline and hydrated and nonhydrated mesostructures have been evaluated in order to favor the posterior in situ polymerization of adsorbed aniline.     

Second-order nonlinear optical properties of the Ag(111)/electrolyte interface in the presence of self-assembled monolayers containing conjugated pi systems. I. Alpha-functionalized terthiophene films on Ag(111)

The nonlinear optical properties of self-assembled monolayers obtained from bonding two different alpha-functionalized terthiophenes (alpha-T3) to (111) silver electrode surfaces have been investigated using second harmonic generation (SHG). The two (alpha-T3) compounds used were functionalized with alkane chains of different lengths (C8 and C4), and each was terminated with a thiol anchoring group. A nitrile group was attached to the terminal thiophene ring of the (alpha-T3) compound with the C4 chain. The orientation of the polarization of the incident beam was changed systematically and gradually between "p" and "s" orientation and the SH signal (isotropic and anisotropic contributions) analyzed in both directions ("P" and "S"). The symmetry of the system was reduced by the presence of the adlayers from C3v to C3. The dependence on the applied potential and the incident wavelength has also been studied. The relative magnitudes and phases of the various second-order tensor elements have been estimated and compared with the values for a bare surface. A resonance process in the (alpha-T3) pi moiety has been investigated, and from this, the effective "band-gap" energies of the organic semiconductor SAMs (i.e., the energy difference between the pi-pi bands) have been estimated.     

Analysis of organic acids in wines by Fourier-transform infrared spectroscopy

Fourier-transform infrared (FTIR) spectroscopy has been a major point of development in many wine laboratories in recent years. It enables almost instant analysis of several properties of wine, usually with very good precision and accurate results. Nevertheless, validation procedures should not be forgotten and should be fully performed. Recovery experiments were performed by spiking wine samples with different amounts of organic acids (tartaric, malic, lactic, acetic and citric—the most prominent in wines). After FTIR analysis of the total acidity and of each organic acid concentration, recoveries were calculated. For total acidity recovery results were, in general, good and very close to 100% (64–111%). On the other hand, for individual organic acid concentrations, the recovery results were lower than 100% (11–73%) for all spiking additions. These results could be explained by spectroscopic interferences between the organic acids. Because they have similar infrared spectra, it is not easy to distinguish between them and, therefore, to achieve accurate calibration. When total acidity, with a different infrared spectrum from the other abundant compounds in the wine, was taken as a single property the recovery results were acceptable.     

A universal temperature controlled membrane interface for the analysis of volatile and semi-volatile organic compounds

A universal temperature controlled membrane interface (TCMI) has been constructed for hollow-fibre membranes. The membrane temperature is controllable in the range -70 to 250 degrees C using an electric heater and a flow of cooled nitrogen or helium gas. Volatile and semi-volatile organic compounds may be detected either by continuous diffusion across the membrane or by in-membrane pre-concentration followed by thermal desorption into the detector. The TCMI interface is demonstrated in combination with mass spectrometry and GC-MS, for the determination of VOCs and SVOCs in aqueous and air samples and for the on-line monitoring of a bioreactor.     

MP2 study of substituent effects of 2-substituted alkyl ethyl methylcarbamates in homogeneous, unimolecular gas phase elimination reaction

Møller-Plesset MP2/6-31G method was used to examine the gas-phase elimination of 2-substituted alkyl ethyl N,N-dimethylcarbamates. The results of these calculations support a concerted non-synchronous six-membered cyclic transition state mechanism for carbamates containing a C_β–H bond at the alkyl side of the ester. These substrates produce the N,N-dimethylcarbamic acid and the corresponding olefin. The unstable intermediate, N,N-dimethylcarbamic acid, rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO₂ gas. Correlation of the logarithm of theoretical rate coefficients against original Taft's σ* values gave an approximate straight line (ρ*=−1.39, r=0.9558 at 360 °C). In addition to this fact, when log k_rel is plotted against the theoretical log k_rel for 2-substituted ethyl N,N-dimethylcarbamates a reasonable straight line (r=0.9919 at 360 °C) is obtained, suggesting similar mechanism.     

Reactions of carbethoxycarbene with enaminones. Formation of unexpected pyrroles

The reactions of carbethoxycarbene (:CH₂-CO₂Et, 2) with several acyclic enaminones (RCOCH=CR¹NHR², 3) lead to the unexpected formation of 2-Me, 3-CO₂Et, 4-H, 5-R¹-pyrroles 4 . Structural variations of the enaminones show that the structural fragments C(3)-CO₂Et and C(2)-Me are provided by 2 and that the fragment C(5)-R¹NHR² originates from the enaminones 3 , while the RCO group from 3 is eliminated during the course of reaction. Reactions with cyclic and nitrogen-hindered enaminones do not lead to pyrrole formation but occur by simple insertion of 2 to the Cα-H bond.     

Photostability of a photochromic naphthopyran dye in different sol-gel prepared ormosil coatings

A photochromic naphthopyran derivative was embedded in sol-gel prepared thin ormosil films. The resulting samples show high transparency and exhibit a strong red colouration upon irradiation with UV light. The photostability of the photochromic molecules is strongly related to the nature of the embedding ormosil matrix. The introduction of organic functional groups into the inner pore surface of the matrix allows tailoring the chemical environment where the dye molecules will be allocated, in terms of the effectiveness of the interaction between the photochromic molecules and the Si-OH groups on the surface of the pores, affecting the stability of the molecules upon prolonged exposition to UV light. The photostability of the molecules was increased in matrices functionalized with larger organic groups, or with larger amount of modifying groups. In this way the photodegradation of the photochromic molecules could be reduced by a factor of 5, as compared with the photodegradation of the molecules in unfunctionalized silica matrix.     

Problem of hidden variables

The problem of hidden variables in quantum mechanics is formalized as follows. A general or contextual (noncontextual) hidden-variables theory is defined as a mappingf: Q×M C (f: QC) whereQ is the set of projection operators in the appropriate (quantum) Hilbert space,M is the set of maximal Boolean subalgebras ofQ andC is a (classical) Boolean algebra. It is shown that contextual (noncontextual) hidden-variables always exist (do not exist).